Polymer solar cell

ABSTRACT

A polymer solar cell includes a photoactive layer, a cathode electrode, and an anode electrode. The photoactive layer includes a polymer layer and a carbon nanotube layer. The polymer layer includes a first polymer surface and a second polymer surface opposite to the first polymer surface. A portion of the carbon nanotube layer is embedded in the polymer layer, and another portion of the carbon nanotube layer is exposed from the polymer layer. The cathode electrode is located a surface of the carbon nanotube layer away from the polymer layer. The anode electrode is located on the first polymer surface and spaced apart from the carbon nanotube layer. The entire second polymer surface is exposed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 16/155,898, filed on Oct. 10, 2018, entitled,“POLYMER SOLAR CELL”, which claims all benefits accruing under 35 U.S.C.§ 119 from China Patent Application No. 201810337312.X, filed on Apr.16, 2018, in the China National Intellectual Property Administration,the contents of which are hereby incorporated by reference. Thisapplication is related to commonly-assigned applications entitled,“POLYMER SOLAR CELL”, concurrently filed Ser. No. 16/155,900; “METHODFOR MAKING POLYMER SOLAR CELL”, concurrently filed Ser. No. 16/155,894;“POLYMER SOLAR CELL”, concurrently filed Ser. No. 16/155,896; “METHODFOR MAKING POLYMER SOLAR CELL”, concurrently filed Ser. No. 16/155,897;“METHOD FOR MAKING POLYMER SOLAR CELL”, concurrently filed Ser. No.16/155,899. Ser. No. 16/155,900 and Ser. No. 16/155,894 share the samespecification, Ser. No. 16/155,896 and Ser. No. 16/155,897 share thesame specification, and Ser. No. 16/155,898 and Ser. No. 16/155,899share the same specification. Disclosures of the above-identifiedapplications are incorporated herein by reference.

FIELD

The present application relates to polymer solar cells and methods formaking the same.

BACKGROUND

The polymer solar cell has many advantages such as wide raw materialsand low cost, and has become one of the research hotspots in recentyears. When the light reaches the photoactive layer of the polymer solarcell, the photoactive layer absorbs photons of the light and generatesexcitons. The excitons diffuse and reach the interface between the donorand the acceptor to form electrons and holes. The electrons pass throughthe acceptor and reach the cathode electrode, and the holes pass throughthe donor and reach the anode electrode. Thus, a potential differencebetween the cathode electrode and the anode electrode is formed. The useof solar light is an important factor to affect the photoelectricconversion efficiency of the polymer solar cell. A common method is toincrease the solar light absorption rate by changing the material of thephotoactive layer.

Al-Haik et la. (US20070110977A1) discloses that a plurality of carbonnanotubes are dispersed in a polymer and then these carbon nanotubes areoriented using a magnetic field, to form a composite. The composite canbe acted as a photoactive material of the polymer solar cell. However,the carbon nanotubes are covered with the polymer, and the carbonnanotubes do not directly contact with the electrodes, thereby reducingthe electrical conductivity between the carbon nanotubes and theelectrodes.

Therefore, there is room for improvement in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures, wherein:

FIG. 1 schematically shows a first embodiment of a polymer solar cell.

FIG. 2 schematically shows a first embodiment of another polymer solarcell.

FIG. 3 is a process flow of a method for making the polymer solar cellof FIG. 1 .

FIG. 4 is a scanning electron microscope (SEM) image of a drawn carbonnanotube film.

FIG. 5 is an SEM image of a flocculated carbon nanotube film.

FIG. 6 is an SEM image of a pressed carbon nanotube film including aplurality of carbon nanotubes arranged along a same direction.

FIG. 7 is an SEM image of a pressed carbon nanotube film including aplurality of carbon nanotubes which is arranged along differentdirection.

FIG. 8 schematically shows a second embodiment of a polymer solar cell.

FIG. 9 schematically shows a third embodiment of a polymer solar cell.

FIG. 10 schematically shows a fourth embodiment of a polymer solar cell.

FIG. 11 schematically shows a fourth embodiment of another polymer solarcell.

FIG. 12 schematically shows a fifth embodiment of a polymer solar cell.

FIG. 13 is a process flow of a method for making the polymer solar cellof FIG. 12 .

FIG. 14 is a process flow of a method for placing a carbon nanotubearray into the polymer solution.

FIG. 15 is a process flow of another method for placing the carbonnanotube array into the polymer solution.

FIG. 16 schematically shows the fifth embodiment of pretreating thecarbon nanotube array.

FIG. 17 schematically shows a sixth embodiment of a polymer solar cell.

FIG. 18 schematically shows a seventh embodiment of a polymer solarcell.

FIG. 19 schematically shows an eighth embodiment of a polymer solarcell.

FIG. 20 schematically shows a ninth embodiment of a polymer solar cell.

FIG. 21 schematically shows a ninth embodiment of a composite structureformed by the anode electrode and a cathode electrode.

FIG. 22 schematically shows along XXII-XXII line of FIG. 20 .

FIG. 23 is a process flow of a method for making the polymer solar cellof FIG. 20 .

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. The drawings are not necessarily to scale, andthe proportions of certain parts may be exaggerated to illustratedetails and features better. The description is not to be considered aslimiting the scope of the embodiments described herein.

Several definitions that apply throughout this disclosure will now bepresented.

The term “substantially” is defined to be essentially conforming to theparticular dimension, shape or other word that substantially modifies,such that the component need not be exact. For example, substantiallycylindrical means that the object resembles a cylinder, but can have oneor more deviations from a true cylinder. The term “comprising” means“including, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in a so-described combination, group,series and the like.

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

FIG. 1 shows a polymer solar cell 100 of a first embodiment and thatincludes an anode electrode 12, a photoactive layer 14, and a cathodeelectrode 18. The photoactive layer 14 includes a polymer layer 142 anda carbon nanotube layer 143. The polymer layer 142 includes a firstpolymer surface 1422 and a second polymer surface 1424 opposite to thefirst polymer surface 1422. The carbon nanotube layer 143 includes aplurality of carbon nanotubes 144. The cathode electrode 18 is locatedon a surface of the carbon nanotube layer 143 away from the polymerlayer 142. The anode electrode 12 is located on the first polymersurface 1422 and spaced apart from the carbon nanotube layer 143.

The polymer layer 142 functions as an electron donor. The material ofthe polymer layer 142 can be polythiophene and its derivative,polyfluorene and its derivative, poly-phenylene vinylene and itsderivative, polypyrrole and its derivative, or any combination thereof.The polythiophene derivative can be poly(3-hexylthiophene) (P₃HT). Thepolyfluorene derivative can be poly(dioctylfluorene). The poly-phenylenevinylene derivative can bepoly[2-methoxy-5-(2-ethyl-hexyloxy)-1,4-phenylene vinylene]. In oneembodiment, the material of the polymer layer 142 is polythiophene.

The plurality of carbon nanotubes 144 functions as electron acceptors.The plurality of carbon nanotubes 144 are substantially parallel to eachother. The plurality of carbon nanotubes 144 are spaced apart from eachother. The length directions of the plurality of carbon nanotubes 144substantially extend along the same direction. The length directions ofthe plurality of carbon nanotubes 144 are parallel to the first polymersurface 1422. Some carbon nanotubes 144 are embedded in the polymerlayer 142, and the rest of carbon nanotubes 144 are exposed from thepolymer layer 142. The carbon nanotubes 144 exposed from the polymerlayer 142 is located on the first polymer surface 1442. The carbonnanotubes 144 can be single-walled, double-walled, multi-walled carbonnanotubes, or their combinations. The single-walled carbon nanotubes 144have a diameter of about 0.5 nanometers (nm) to about 50 nm. Thedouble-walled carbon nanotubes 144 have a diameter of about 1.0 nm toabout 50 nm. The multi-walled carbon nanotubes 144 have a diameter ofabout 1.5 nm to about 50 nm. The lengths of the carbon nanotubes 144 aresubstantially equal. In one embodiment, the carbon nanotube layer 143 isa multi-layer stacked drawn carbon nanotube film.

There are carbon nanotubes 144 between the cathode electrode 18 and thefirst polymer surface 1422, thus the cathode electrode 18 is not indirect contact with the first polymer surface 1422, thereby preventingholes generated by the exciton separation from migrating from thepolymer layer 142 to the cathode electrode 18. Thus, all of the holescan migrate from the polymer layer 142 to the anode electrode 12. Theanode electrode 12 is spaced apart from with the carbon nanotubes 144,thereby preventing electrons generated by the exciton separation frommigrating from the carbon nanotubes 144 to the anode electrode 12. Thus,all of the electrons can migrate from the carbon nanotubes 144 to thecathode electrode 18. The anode electrode 12 and the cathode electrode18 can be a transparent conductive layer or a porous mesh structure,such as ITO (indium tin oxide) layer, FTO (F-doped tin oxide) layer, orthe like. The anode electrode 12 and the cathode electrode 18 can beopaque, such as aluminum layer, silver layer, or the like.

Both the anode electrode 12 and the cathode electrode 18 are located onthe same side of the polymer layer 142 (i.e., on the first polymersurface 1422). Thus, light can reach the photoactive layer 14 from thesecond polymer surface 1424, and accordingly, the anode electrode 12 andthe cathode electrode 18 do not have to be transparent. In oneembodiment, light reaches the photoactive layer 14 from the secondpolymer surface 1424, and the materials of the anode electrode 12 andthe cathode electrode 18 are aluminum. The shapes of the anode electrode12 and the cathode electrode 18 are not limited. The larger the contactarea of the cathode electrode 18 and the carbon nanotube layer 143, thefaster the speed of electrons that migrate to the cathode electrode 18.The smaller the contact area of the anode electrode 12 and the firstpolymer surface 1422, the slower the speed of holes that migrate to theanode electrode 12. In one embodiment, the anode electrode 12 has a ringshape, such as circular ring, as shown in FIG. 2 .

When any one of the anode electrode 12 and the cathode electrode 18 is ametal film, the metal film can reflect light that reaches the metal filminto the photoactive layer 14, improving the light use. Thus, the metalfilm plays a function of conducting electron and reflecting light.

FIG. 3 shows a method for making the polymer solar cell 100. Dependingon the embodiment, certain of the steps or blocks described may beremoved, others may be added, and the sequence of steps or blocks may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some reference numeral indicationreferring to certain blocks or steps. However, the reference numeralindication used is only for identification purposes and not interpretedas a suggestion as to an order for the steps. The method includes thefollowing steps:

S11, placing the carbon nanotube layer 143 into a polymer solution 22,wherein the carbon nanotube layer 143 includes the plurality of carbonnanotubes 144, the length direction of each carbon nanotube 144 isparallel to the surface of the polymer solution 22, some carbonnanotubes 144 are immersed in the polymer solution 22, and some carbonnanotubes 144 are exposed from the polymer solution 22;

S12, curing the polymer solution 22 to form the polymer layer 142,wherein the polymer layer 142 includes a first polymer surface 1422 anda second polymer surface 1424 opposite to the first polymer surface1422, the area of the first polymer surface 1422 is greater than thearea of the surface of the carbon nanotube layer 143 away from thepolymer layer 142, some carbon nanotubes 144 are embedded in the polymerlayer 142, and some carbon nanotubes 144 are exposed from the polymerlayer 142; and

S13, forming the cathode electrode 18 on the surface of the carbonnanotube layer 143 away from the polymer layer 142, and forming theanode electrode 12 on the first polymer surface 1422, wherein the anodeelectrode 12 is spaced apart from the carbon nanotube layer 143.

In the step S11, the carbon nanotube layer 143 includes a plurality ofcarbon nanotube films stacked on each other. The carbon nanotube filmcan be a drawn carbon nanotube film, a flocculated carbon nanotube film,or a pressed carbon nanotube film.

FIG. 4 shows the drawn carbon nanotube film, and the drawn carbonnanotube film includes the plurality of successive and oriented carbonnanotubes 144 joined end-to-end by van der Waals attractive force therebetween. The carbon nanotubes 144 in the drawn carbon nanotube film areoriented along a preferred orientation. The carbon nanotubes 144 areparallel to a surface of the drawn carbon nanotube film. The drawncarbon nanotube film is a free-standing film. The drawn carbon nanotubefilm can bend to desired shapes without breaking. A film can be drawnfrom a carbon nanotube array to form the drawn carbon nanotube film.

If the carbon nanotube layer 143 includes at least two stacked drawncarbon nanotube films, adjacent drawn carbon nanotube films can becombined by only the van der Waals attractive force there between.Additionally, when the carbon nanotubes 144 in the drawn carbon nanotubefilm are aligned along one preferred orientation, an angle can existbetween the orientations of carbon nanotubes 144 in adjacent drawncarbon nanotube films, whether stacked or adjacent. An angle between thealigned directions of the carbon nanotubes 144 in two adjacent drawncarbon nanotube films can be in a range from about 0 degree to about 90degrees. The number of the drawn carbon nanotube films in the carbonnanotube layer 143 can be in a range from 2 to 200. In one embodiment,the carbon nanotube layer 143 includes three layers of the drawn carbonnanotube films, and the angle between the aligned directions of thecarbon nanotubes 144 in two adjacent drawn carbon nanotube films isabout 90 degrees.

FIG. 5 shows the flocculated carbon nanotube film, and the flocculatedcarbon nanotube film includes a plurality of long, curved, disorderedcarbon nanotubes 144 entangled with each other. The flocculated carbonnanotube film can be isotropic. The carbon nanotubes 144 can besubstantially uniformly dispersed in the flocculated carbon nanotubefilm. Adjacent carbon nanotubes 144 are acted upon by van der Waalsattractive force to obtain an entangled structure. Due to the carbonnanotubes 144 in the flocculated carbon nanotube film being entangledwith each other, the flocculated carbon nanotube film has excellentdurability, and can be fashioned into desired shapes with a low risk tothe integrity of the flocculated carbon nanotube film. Further, theflocculated carbon nanotube film is a free-standing film.

FIGS. 6 and 7 show the pressed carbon nanotube film, and the pressedcarbon nanotube film includes the plurality of carbon nanotubes 144. Thecarbon nanotubes 144 in the pressed carbon nanotube film can be arrangedalong a same direction, as shown in FIG. 6 . The carbon nanotubes 144 inthe pressed carbon nanotube film can be arranged along differentdirections, as shown in FIG. 7 . The carbon nanotubes 144 in the pressedcarbon nanotube film can rest upon each other. An angle between aprimary alignment direction of the carbon nanotubes 144 and a surface ofthe pressed carbon nanotube film is about 0 degree to approximately 15degrees. The greater the pressure applied, the smaller the angleobtained. If the carbon nanotubes 144 in the pressed carbon nanotubefilm are arranged along different directions, the pressed carbonnanotube film can have properties that are identical in all directionssubstantially parallel to the surface of the pressed carbon nanotubefilm. Adjacent carbon nanotubes 144 are attracted to each other and arejoined by van der Waals attractive force. Therefore, the pressed carbonnanotube film is easy to bend to desired shapes without breaking.Further, the pressed carbon nanotube film is a free-standing film.

The term “free-standing” includes, but not limited to, the drawn carbonnanotube film, the flocculated carbon nanotube film, or the pressedcarbon nanotube film that does not have to be supported by a substrate.For example, the drawn carbon nanotube film, the flocculated carbonnanotube film, or the pressed carbon nanotube film can sustain theweight of itself when it is hoisted by a portion thereof without anysignificant damage to its structural integrity. So, if the drawn carbonnanotube film, the flocculated carbon nanotube film, or the pressedcarbon nanotube film is placed between two separate supporters, aportion of the drawn carbon nanotube film, the flocculated carbonnanotube film, or the pressed carbon nanotube film, not in contact withthe two supporters, would be suspended between the two supporters andyet maintain film structural integrity.

The polymer solution 22 is formed by dispersing a polymer material in anorganic solvent. The organic solvent is not limited as long as thepolymer can be dissolved in the organic solvent.

In the step S12, the method for curing the polymer solution 22 is notlimited, for example, polymer solution 22 is heated to form the polymerlayer 142. In one embodiment, the length direction of each carbonnanotube 144 is parallel to the first polymer surface 1422.

In the step S13, the methods for forming the cathode electrode 18 andanode electrode 12 are not limited, such as sputtering, coating, vapordeposition, or spraying. There are gaps between adjacent carbonnanotubes 144, a previously prepared cathode electrode 18, such as ametal piece, can be directly located on the surface of the carbonnanotube layer 143 away from the polymer layer 142. Thus, the materialof the cathode electrode 18 do not pass through the gaps to directlycontact with the polymer layer 142.

FIG. 8 shows a polymer solar cell 200 of a second embodiment. Thepolymer solar cell 200 of the second embodiment is similar to thepolymer solar cell 100 of the first embodiment above except that thepolymer solar cell 200 further includes a reflective layer 24 located onthe surface of the cathode electrode 18 away from the polymer layer 142,and the second polymer surface 1424 is the incident surface of light.When the surface of the cathode electrode 18 away from the polymer layer142 is used as the incident surface of light, the reflective layer 24should be located on the second polymer surface 1424.

The function of the reflective layer 24 is: when light reaches thephotoactive layer 14 from the second polymer surface 1424, part of thelight that reaches the cathode electrode 18 can be reflected back intothe photoactive layer 14 from the cathode electrode 18 by the reflectivelayer 24 located on the surface of the cathode electrode 18 away fromthe polymer layer 142. Thus, the light use is improved. When lightreaches the photoactive layer 14 from the cathode electrode 18, the lostlight from the second polymer surface 1424 can be reflected back intothe photoactive layer 14 by the reflective layer 24 located on thesecond polymer surface 1424. Thus, the light use is improved. Thematerial of the photoactive layer 14 has a high reflectivity, and thematerial can be, but is not limited to, a metal or metal alloy. Themetal can be gold, silver, aluminum, or calcium. The metal alloy can bean alloy of calcium and aluminum, an alloy of magnesium and silver, orthe like.

In the second embodiment, the method for making the polymer solar cell200 is provided. The method for making the polymer solar cell 200 in thesecond embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the method for makingthe polymer solar cell 200 further includes a step of forming thereflective layer 24. The method for forming the reflective layer 24 isnot limited, such as sputtering, coating, vapor deposition, or the like.

FIG. 9 shows a polymer solar cell 300 of a third embodiment. The polymersolar cell 300 of the third embodiment is similar to the polymer solarcell 100 of the first embodiment above except that the polymer solarcell 300 further includes an exciton blocking layer 26. The excitonblocking layer 26 can be located between the polymer layer 142 and anodeelectrode 12. The exciton blocking layer 26 can also be located betweenthe carbon nanotube layer 143 and the cathode electrode 18.

The function of the exciton blocking layer 26 is: light reaches thephotoactive layer 14 to form excitons, and the exciton blocking layer 26prevents the excitons from diffusing toward the cathode electrode 18 orthe anode electrode 12, thereby making all excitons reach the interfacebetween the donor and the acceptor. Thus, the utilization ratio of theexcitons is improved, and accordingly the efficiency of photoelectricconversion of the polymer solar cell 300 is also improved. The materialof the exciton blocking layer 26 is organic material, such asZn₄O(AID)₆, BAlQ₃, BCP, Bphen, Alq₃, TAZ, or TPBI.

In the third embodiment, the method for making the polymer solar cell300 is provided. The method for making the polymer solar cell 300 in thethird embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the method for makingthe polymer solar cell 300 further includes a step of forming theexciton blocking layer 26. After curing the polymer solution 22 andbefore forming the cathode electrode 18 and the anode electrode 12, theexciton blocking layer 26 is formed on the first polymer surface 1422 orthe surface of the carbon nanotube layer 143 away from the polymer layer142 by sputtering, coating, vapor deposition, or the like.

FIG. 10 shows a polymer solar cell 400 of a fourth embodiment. Thepolymer solar cell 400 of the fourth embodiment is similar to thepolymer solar cell 100 of the first embodiment above except that thepositons of the anode electrodes 12. In the polymer solar cell 100, theanode electrode 12 and the cathode electrode 18 are located on the sameside of the polymer layer 142 (i.e., on the first polymer surface 1422).However, in the polymer solar cell 400, the anode electrode 12 and thecathode electrode 18 are located on different sides of the polymer layer142. The polymer layer 142 further includes a third polymer surface 1426and a fourth polymer surface 1428, and the third polymer surface 1426and the fourth polymer surface 1428 are connected to the first polymersurface 1422 and the second polymer surface 1424. The anode electrode 12is located on the third polymer surface 1426 or the fourth polymersurface 1428. The anode electrode 12 can be a ring, and surround theentire side surface of the polymer layer 142, as shown in FIG. 11 .

In the fourth embodiment, the method for making the polymer solar cell400 is provided. The method for making the polymer solar cell 400 in thefourth embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that in the method formaking the polymer solar cell 400, the anode electrode 12 is formed onthe third polymer surface 1426 or the fourth polymer surface 1428.

FIG. 12 shows a polymer solar cell 500 of a fifth embodiment. Thepolymer solar cell 500 of the fifth embodiment is similar to the polymersolar cell 100 of the first embodiment above except that the polymersolar cell 500 further includes an insulating layer 16 and the lengthdirections of the carbon nanotubes 144 are perpendicular to the firstpolymer surface 1422. In the polymer solar cell 500, the insulatinglayer 16 is located between the cathode electrode 18 and the polymerlayer 142, and the insulating layer 16 is in direct contact with thecathode electrode 18 and the polymer layer 142. In the polymer solarcell 500, the carbon nanotubes 144 are exposed from the polymer layer142, pass through the insulating layer 16, and are in direct contactwith the cathode electrode 18. Each carbon nanotube 144 of the polymersolar cell 500 includes a first end 1442 and a second end 1444 oppositeto the first end 1442, the first end 1442 is embedded in the cathodeelectrode 18, and the second end 1444 is embedded in the polymer layer142. Each carbon nanotube 144 consists of a first carbon nanotubeportion, a second carbon nanotube portion, and a third carbon nanotubeportion. The first carbon nanotube portion is embedded in the polymerlayer 142, the second carbon nanotube portion is embedded in theinsulating layer 16, and the third carbon nanotube portion is embeddedin the cathode electrode 18.

The function of the insulating layer 16 is to electrically insulate thepolymer layer 142 from the cathode electrode 18, thereby preventingholes generated by the exciton separation from migrating from thepolymer layer 142 to the cathode electrode 18. Thus, all of the holescan migrate from the polymer layer 142 to the anode electrode 12. Theinsulating layer 16 can be transparent or opaque. When the surface ofthe cathode electrode 18 away from the insulating layer 16 is theincident surface of light, the insulating layer 16 needs to betransparent. When the second polymer surface 1424 is the incidentsurface of light, the insulating layer 16 can be transparent or opaque.The material of the transparent insulating layer 16 is not limited, suchas polymethyl methacrylate (PMMA), polycarbonate (PC),polyperfluoroethylene propylene (FEP), or polyvinyl fluoride (PVF). Thematerial of the opaque insulating layer 16 is not limited, such assilica gel. The main component of the silica gel is silica. In oneembodiment, the material of the insulating layer 16 is PMMA.

The polymer solar cell 500 further includes a reflective layer locatedon the surface of the cathode electrode 18 away from the insulatinglayer 16, or located on the second polymer surface 1424.

The polymer solar cell 500 further includes an exciton blocking layer.The exciton blocking layer can be located between the first polymersurface 1422 and anode electrode 12. The exciton blocking layer can alsobe located between the photoactive layer 14 and the insulating layer 16,or between the insulating layer 16 and the cathode electrode 18. Whenthe exciton blocking layer is located between the photoactive layer 14and the insulating layer 16, the carbon nanotubes 144 pass through theexciton blocking layer and the insulating layer 16, to be in directcontact with the cathode electrode 18.

Both the anode electrode 12 and the cathode electrode 18 are located onthe same side of the polymer layer 142 (i.e., on the first polymersurface 1422). Thus light can reach the photoactive layer 14 from thesecond polymer surface 1424, and accordingly, the anode electrode 12,the cathode electrode 18, and the insulating layer 16 do not have to betransparent. In addition, the conductivity in the length direction ofthe carbon nanotubes 144 is good, and the conductivity in the directionperpendicular to the length direction of the carbon nanotubes 144 ispoor, thus when the first ends 1442 are exposed from the polymer layer142 and the insulating layer 16 to be in direct contact with the cathodeelectrode 18, the electrical conductivity between the carbon nanotubes144 and the cathode electrode 18 is improved.

FIG. 13 shows a method for making the polymer solar cell 500. Dependingon the embodiment, certain of the steps or blocks described may beremoved, others may be added, and the sequence of steps or blocks may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some reference numeral indicationreferring to certain blocks or steps. However, the reference numeralindication used is only for identification purposes and not interpretedas a suggestion as to an order for the steps. The method includes thefollowing steps:

S51, placing a carbon nanotube array 20 into a polymer solution 22,wherein the carbon nanotube array 20 includes the plurality of carbonnanotubes 144, each of the plurality of carbon nanotubes 144 has thefirst end 1442 and the second end 1444 opposite to the first end 1442,the first end 1442 is exposed out of the polymer solution 22, and thesecond end 1444 is immersed in the polymer solution 22;

S52, curing the polymer solution 22 to form the polymer layer 142,wherein polymer layer 142 includes the first polymer surface 1422 andthe second polymer surface 1424 opposite to the first polymer surface1422, the first end 1442 is exposed out of the polymer layer 142, andthe second end 1444 is embedded in the polymer layer 142;

S53, forming the insulating layer 16 on the first polymer surface 1422,wherein the first end 1442 passes through the insulating layer 16 andexposed out of the insulating layer 16;

S54, forming the cathode electrode 18 on a surface of the insulatinglayer 16 away from the polymer layer 142, wherein the first end 1442 isembedded in the cathode electrode 18; and

S15, forming the anode electrode 12 on the first polymer surface 1422,wherein the anode electrode 12 is spaced apart from the plurality ofcarbon nanotubes 144.

In the step S51, the carbon nanotube array 20 has a first surface 202and a second surface 204 opposite to the first surface 202, and theplurality of carbon nanotubes 144 extend from the first surface 202 tothe second surface 204. The plurality of carbon nanotubes 144 aresubstantially parallel to and spaced apart from each other. The firstends 1442 of all of the carbon nanotubes 144 form the first surface 202,and the second ends 1444 of all of the carbon nanotubes 144 form thesecond surface 204. The length directions of the carbon nanotubes 144are substantially perpendicular to the first surface 202. In oneembodiment, the length directions of the carbon nanotubes 144 areperpendicular to the first surface 202, and the carbon nanotubes 144 areparallel to each other. The lengths of the carbon nanotubes 144 aregreater than or equal to 100 nanometers. In one embodiment, the lengthsof the carbon nanotubes 144 are several hundred micrometers to severalhundred millimeters. In one embodiment, the lengths of the carbonnanotubes 144 are greater than or equal to 100 nanometers and less thanor equal to 10 millimeters, such as 100 micrometers, 500 micrometers,1000 micrometers, or 5 millimeters.

The method for placing the carbon nanotube array 20 into the polymersolution 22 is not limited. The present invention provides two methods,but the two methods do not limit the invention.

FIG. 14 shows a method for placing the carbon nanotube array 20 into thepolymer solution 22. Depending on the embodiment, certain of the stepsor blocks described may be removed, others may be added, and thesequence of steps or blocks may be altered. It is also to be understoodthat the description and the claims drawn to a method may include somereference numeral indication referring to certain blocks or steps.However, the reference numeral indication used is only foridentification purposes and not interpreted as a suggestion as to anorder for the steps. The method includes the following steps:

S511, growing the carbon nanotube array 20 on a growth substrate 30,wherein the first end 1442 of each carbon nanotube 144 is in directcontact with the growth substrate 30, the second end 1444 of each carbonnanotube 144 is away from the growth substrate 30;

S512, placing the polymer solution 22 in a container 28; and

S513, inverting the growth substrate 30 to make a portion of each carbonnanotube 144 immersed in the polymer solution 22, wherein the second end1444 is also immersed in the polymer solution 22.

In the step S511, the method for making the carbon nanotube array 20includes the following steps: (a) providing a flat growth substrate 30,wherein the growth substrate 30 can be a P-type silicon wafer, an N-typesilicon wafer or a silicon wafer formed with an oxidized layer thereon;and in one embodiment, a 4-inch, P-type silicon wafer is used as thegrowth substrate 30; (b) forming a catalyst layer on the growthsubstrate 30, wherein the catalyst layer is made of a material selectedfrom the group consisting of iron (Fe), cobalt (Co), nickel (Ni), and analloy thereof; (c) annealing the growth substrate 30 with the catalystlayer in air at a temperature in a range from 700° C. to 900° C. forabout 30 minutes to about 90 minutes; (d) providing a carbon source gasat high temperature to a furnace for about 5 minutes to about 30 minutesto grow the carbon nanotube array 20 on the growth substrate 30.

In the step S513, the method for inverting the growth substrate 30 andpartially immersing the carbon nanotube array 20 into the polymersolution 22 is not limited. For example, the growth substrate 30 can befixed by a tool, such as tweezers, to invert the growth substrate 30.

It can be understood that, when the carbon nanotube array 20 is placedin the polymer solution 22 by the first method, it is necessary tofurther include a step of removing the growth substrate 30 before thestep S13. The method for removing the growth substrate 30 is notlimited, for example, the growth substrate 30 is peeled off using atool, such as a knife, or the growth substrate 30 is etched using alaser.

FIG. 15 shows another method for placing the carbon nanotube array 20into the polymer solution 22. Depending on the embodiment, certain ofthe steps or blocks described may be removed, others may be added, andthe sequence of steps or blocks may be altered. It is also to beunderstood that the description and the claims drawn to a method mayinclude some reference numeral indication referring to certain blocks orsteps. However, the reference numeral indication used is only foridentification purposes and not interpreted as a suggestion as to anorder for the steps. The method includes the following steps:

S511′, growing the carbon nanotube array 20 on a growth substrate 30,wherein the first end 1442 of each carbon nanotube 144 is in directcontact with the growth substrate 30, the second end 1444 of each carbonnanotube 144 is away from the growth substrate 30;

S512′, removing the growth substrate 30;

S513′, placing the polymer solution 22 in the container 28; and

S514′, immersing a portion of each carbon nanotube 144 in the polymersolution 22.

In the step S512′, the carbon nanotube array 20 can be totally peeledoff from the growth substrate 30. In one embodiment, the carbon nanotubearray 20 is totally peeled off from the growth substrate 30 by a knifeor other similar tool along a direction parallel to the surface of thegrowth substrate 30. In the process of peeling off the carbon nanotubearray 20, adjacent two of the carbon nanotubes 144 join together by vander Waals attractive force, therefore the carbon nanotube array 20 isfree-standing structure. In one embodiment, two tweezers respectivelyclamp the two opposite sides of the carbon nanotube array 20.

The term “free-standing” includes, but not limited to, the carbonnanotube array 20 that does not have to be supported by a substrate. Forexample, a free-standing carbon nanotube array 20 can sustain itselfwhen it is hoisted by a portion thereof without any significant damageto its structural integrity. So, if the free-standing carbon nanotubearray 20 is placed between two separate substrates, a portion of thefree-standing carbon nanotube array 20, not in contact with the twosubstrates, would be suspended between the two substrates and yetmaintain structural integrity.

It can be understood that after curing the polymer solution 22 to formthe polymer layer 142 in the step S12 and before combining the polymerlayer 142 with the anode electrode 12 in the step S16, a step ofremoving the container 28 is needed. For example, the whole structure inthe container 28 is taken out of the container 28. In addition, themethod for curing the polymer solution 22 is not limited, for example,polymer solution 22 is heated to form the polymer layer 142.

In the step S53, the method for forming the insulating layer 16 is notlimited. For example, the insulating layer 16 is first dissolved in asolvent to form a solution, and then the solution is sprayed or spincoated on the first polymer surface 1422 of the polymer layer 142. Inone embodiment, PMMA is dissolved in the organic solvent to form a PMMAsolution, and the PMMA solution is coated on the first polymer surface1422. Then the PMMA solution penetrates into the gas between adjacentcarbon nanotube 144. The height of the PMMA solution is less than thelength of the carbon nanotube 144 exposed from the polymer layer 142.After curing, the PMMA solution forms a PMMA insulating layer, and thethickness of the PMMA insulating layer is less than the length of thecarbon nanotube 144 exposed from the polymer layer 142. The first end1442 of the carbon nanotube 144 passes through the PMMA insulating layerand is exposed out of the PMMA insulating layer.

In the step S54, the method for forming the cathode electrode 18 on thesurface of the insulating layer 16 away from the polymer layer 142 isnot limited, as sputtering, coating, vapor deposition, or spraying. Apreviously prepared cathode electrode 18, such as a metal piece, can bedirectly located on the surface of the insulating layer 16 away from thepolymer layer 142. The cathode electrode 18 has a thickness such thatthe first end 1442 of the carbon nanotube 144 is embedded in the cathodeelectrode 18 and is covered by the cathode electrode 18.

In the step S54, the method for forming the anode electrode 12 on thefirst polymer surface 1422 is not limited, such as sputtering, coating,vapor deposition, mask etching, spraying, or inkjet printing.

Furthermore, before curing the polymer solution 22, a step ofpretreating the carbon nanotube array 20 can be included. FIG. 16 showsthe method of pretreating the carbon nanotube array 20, and the methodincludes the following steps: (1) adhering the carbon nanotube array 20to a surface of an elastic support 40, wherein the length direction ofeach carbon nanotube 144 is substantially perpendicular to the surfaceof the elastic support 40, and the carbon nanotube array 20 is adheredto the elastic support 40 by an adhesive in one embodiment; (2)respectively pulling the two opposite ends of the elastic support 40along opposite directions. Under the pulling force, the elastic support40 is stretched, the carbon nanotube array 20 is also stretched, and thedistance between two adjacent carbon nanotubes 144 becomes longer. Thepulling speed can be selected according to the carbon nanotube array 20.If the pulling speed is too large, the carbon nanotube array 20 would beeasily broken. In one embodiment, the pulling speed is less than 2 cm/s.The advantage of pretreating the carbon nanotube array 20 is: afterstretching the carbon nanotube array 20, the distance between twoadjacent carbon nanotubes 144 becomes longer, thus the material of theinsulating layer 16 is easy to enter the gap between two adjacent carbonnanotubes 144. The elastic support 40 has better elasticity, and theshape and structure of the elastic support 40 are not limited. Theelastic support 40 can be a planar structure or a curved structure. Theelastic support 40 can be an elastic rubber, a rubber band, or the like.The elastic support 40 is used to support and stretch the carbonnanotube array 20. It can be understood that after pretreating thecarbon nanotube array 20, a step of removing the elastic support 40 isfurther included.

FIG. 17 shows a polymer solar cell 600 of a sixth embodiment. Thepolymer solar cell 600 of the sixth embodiment is similar to the polymersolar cell 500 of the fifth embodiment above except that the positons ofthe anode electrodes 12 in the polymer solar cells 500 and 600 aredifferent. In the polymer solar cell 500, the anode electrode 12 and thecathode electrode 18 are located on the same side of the polymer layer142 (i.e., on the first polymer surface 1422). However, in the polymersolar cell 600, the anode electrode 12 and the cathode electrode 18 arelocated on different sides of the polymer layer 142. The anode electrode12 is located on the third polymer surface 1426 or the fourth polymersurface 1428.

In the sixth embodiment, the method for making the polymer solar cell600 is provided. The method for making the polymer solar cell 600 in thesixth embodiment is similar to the method for making the polymer solarcell 500 in the fifth embodiment above except that in the method formaking the polymer solar cell 600, the anode electrode 12 is formed onthe third polymer surface 1426 or the fourth polymer surface 1428.

FIG. 18 shows a polymer solar cell 700 of a seventh embodiment. Thepolymer solar cell 700 of the seventh embodiment is similar to thepolymer solar cell 500 of the fifth embodiment above except that in thepolymer solar cell 700, the first end 1442 of the carbon nanotube 144 isflush with the surface of the insulating layer 16 away from the polymerlayer 142; and the first end 1442 of the carbon nanotube 144 is indirect contact with the surface of the cathode electrode 18, and is notembedded into the interior of the cathode electrode 18.

In the seventh embodiment, the method for making the polymer solar cell700 is provided. The method for making the polymer solar cell 700 in theseventh embodiment is similar to the method for making the polymer solarcell 500 in the fifth embodiment above except that the insulating layer16 is formed by sputtering, coating, vapor deposition, mask etching,spraying, or inkjet printing, the insulating layer 16 covers the carbonnanotube 144, but the first end 1442 of carbon nanotube 144 is exposed,and the first end 1442 is flush with the surface of the insulating layer16 away from the polymer layer 142. Because the first end 1442 is flushwith the surface of the insulating layer 16 away from the polymer layer142, the cathode electrode 18 is located on the insulating layer 16 awayfrom the polymer layer 142, the first end 1442 is in direct contact withthe surface of the cathode electrode 18 and is not embedded into theinterior of the cathode electrode 18.

FIG. 19 shows a polymer solar cell 800 of an eighth embodiment. Thepolymer solar cell 800 of the eighth embodiment is similar to thepolymer solar cell 500 of the fifth embodiment above except that thearrangement of the carbon nanotubes 144. In the polymer solar cell 500of the fifth embodiment, the length directions of the carbon nanotubes144 is substantially perpendicular to the first polymer surface 1422 ofthe polymer layer 142. In the polymer solar cell 800 of the eighthembodiment, the length directions of the carbon nanotubes 144 and thefirst polymer surface 1422 form an angle that is greater than 0 degreesand less than 90 degrees. In one embodiment, the angle is greater than30 degrees and less than 60 degrees. The advantage of the polymer solarcell 800 is: the carbon nanotubes 144 are tilted in the polymer layer142, thus the surface of the carbon nanotubes 144 (acceptor) in contactwith the polymer layer 142 (donor) is increased. It is beneficial forseparating more excitons into electrons and holes. Thus, thephotoelectric conversion efficiency of the polymer solar cell 800 isimproved.

In the eighth embodiment, the method for making the polymer solar cell800 is provided. The method for making the polymer solar cell 800 in theeighth embodiment is similar to the method for making the polymer solarcell 500 in the fifth embodiment above except that the method for makingthe polymer solar cell 800 further includes a step of pressing thecarbon nanotube array 20 before curing the polymer solution 22. Thecarbon nanotube array 20 can be pressed by a pressing device, such thatthe carbon nanotubes 144 are tilted. The degree of inclination of thecarbon nanotubes 144 can be controlled by controlling the pressure, suchthat the angle of greater than 0 degrees and less than 90 degrees isformed between the first polymer surface 1422 and the carbon nanotubes144.

FIG. 20 -FIG. 23 show a polymer solar cell 900 of a ninth embodiment.The polymer solar cell 900 of the ninth embodiment is similar to thepolymer solar cell 100 of the first embodiment above except that theshapes of the anode electrode 12 and the cathode electrode 18.

In the polymer solar cell 900, the carbon nanotube layer 143 exposedfrom the polymer layer 142 includes a plurality of sub-carbon nanotubelayers 1432, the anode electrode 12 includes a plurality of sub-anodeelectrodes 122, and the cathode electrode 18 includes a plurality ofsub-cathode electrodes 182. The plurality of sub-anode electrodes 122and the plurality of sub-cathode electrodes 182 are spaced apart fromeach other and alternately disposed on the first polymer surface 1422.The plurality of sub-anode electrodes 122 are electrically connected toeach other, and the plurality of sub-cathode electrodes 182 areelectrically connected to each other. In one embodiment, the pluralityof sub-anode electrodes 122 are electrically connected by the connectionportion 502, and the plurality of sub-cathode electrodes 182 areelectrically connected by the connection portion 502, as shown in FIG.21 . The connection portion 502 is made of a conductive material, suchas metal or the like. The plurality of sub-anode electrodes 122 can beintegrally formed with the connection portions 502, and the plurality ofsub-cathode electrodes 182 can be integrally formed with the connectionportions 502, to form comb-teeth electrodes.

FIG. 22 schematically shows along XXII-XXII line of FIG. 20 . In orderto clearly show the positional relationship between the sub-carbonnanotube layer 1432, the sub-anode electrode 122, and the sub-cathodeelectrode 182, the connection portions 502 are omitted in the FIG. 22 .FIG. 22 schematically shows the carbon nanotube layer 143 exposed fromthe polymer layer 142, and the carbon nanotube layer 143 exposed fromthe polymer layer 142 includes the plurality of sub-carbon nanotubelayer 1432 spaced apart from each other, each sub-cathode electrode 182is located on a surface of the sub-carbon nanotube layer 1432 away fromthe polymer layer 142. The plurality of sub-carbon nanotube layer 1432and the plurality of sub-anode electrodes 122 are spaced apart from eachother and alternately disposed on the first polymer surface 1422. It canbe understood that in order to make the sub-anode electrode 122 bespaced apart from the carbon nanotube layer 143, some portions of thepolymer layer 142 are etched so that the first polymer surface 1422 isuneven, as shown in FIG. 22 .

In the ninth embodiment, FIG. 23 shows the method for making the polymersolar cell 900. The method for making the polymer solar cell 900 in theninth embodiment is similar to the method for making the polymer solarcell 100 in the first embodiment above except that the carbon nanotubelayer 143 exposed from the polymer layer 142 is patterned. After curingthe polymer solution 22 to form the polymer layer 142, the carbonnanotube layer 143 exposed from the polymer layer 142 is patterned toform the plurality of sub-carbon nanotube layer 1432 spaced apart fromeach other. Then, the sub-cathode electrode 182 is formed on the surfaceof each sub-carbon nanotube layer 1432 away from the polymer layer 142,and the sub-anode electrode 122 is formed between two adjacentsub-carbon nanotube layer 1432. The sub-anode electrode 122 is spacedapart from the sub-carbon nanotube layer 1432. The cathode electrode 18and the carbon nanotube layer 143 exposed from the polymer layer 142have the same shape.

The polymer solar cells 100 to 900 have the following advantages: 1) thecarbon nanotubes 144 are exposed from the polymer layer 142 to be indirect contact with the cathode electrode 18, improving the electricalconductivity between the carbon nanotubes 144 and the cathode electrode18; 2) the carbon nanotubes 144 of the drawn carbon nanotube film, theflocculated carbon nanotube film, the pressed carbon nanotube film, orthe carbon nanotube array 20 are aligned themselves, and it is no longernecessary to orient the carbon nanotubes 144 by external force, such asa magnetic field; 3) both the anode electrode 12 and cathode electrode18 can be opaque or transparent.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, including inmatters of shape, size and arrangement of the parts within theprinciples of the present disclosure up to, and including, the fullextent established by the broad general meaning of the terms used in theclaims.

Additionally, it is also to be understood that the above description andthe claims drawn to a method may comprise some indication in referenceto certain steps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

What is claimed is:
 1. A polymer solar cell, comprising: a photoactive layer comprising a polymer layer and a carbon nanotube layer, wherein the polymer layer comprises a first polymer surface, a second polymer surface opposite to the first polymer surface, and a side surface connecting the first polymer surface and the second polymer surface; and a portion of the carbon nanotube layer is embedded in the polymer layer, and another portion of the carbon nanotube layer is exposed from the polymer layer; a cathode electrode located a surface of the carbon nanotube layer away from the polymer layer; and an anode electrode located on the side surface and spaced apart from the carbon nanotube layer, wherein the anode electrode surrounds the entire side surface of the polymer layer.
 2. The polymer solar cell of claim 1, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, and length directions of the plurality of carbon nanotubes are parallel to the first polymer surface.
 3. The polymer solar cell of claim 1, further comprising an insulating layer located between the cathode electrode and the polymer layer.
 4. The polymer solar cell of claim 3, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, length directions of the plurality of carbon nanotubes are substantially perpendicular to the first polymer surface, and a portion of each of the plurality of carbon nanotubes is embedded in the cathode electrode.
 5. The polymer solar cell of claim 3, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, length directions of the plurality of carbon nanotubes are substantially perpendicular to the first polymer surface, and an end of each of the plurality of carbon nanotubes is flush with a surface of the insulating layer away from the polymer layer.
 6. The polymer solar cell of claim 3, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, and an angle of greater than 0 degrees and less than 90 degrees is formed between length directions of the plurality of carbon nanotubes and the first polymer surface.
 7. The polymer solar cell of claim 1, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, and length directions of the plurality of carbon nanotubes are substantially parallel to each other.
 8. The polymer solar cell of claim 1, wherein the anode electrode and the cathode electrode are located on different sides of the polymer layer.
 9. The polymer solar cell of claim 1, wherein the carbon nanotube layer comprises a plurality of carbon nanotubes, and the plurality of carbon nanotubes is joined end-to-end by van der Waals attractive force.
 10. The polymer solar cell of claim 1, further comprising a reflective layer located on a surface of the cathode electrode away from the polymer layer.
 11. The polymer solar cell of claim 1, further comprising an exciton blocking layer located between the carbon nanotube layer and the cathode electrode.
 12. The polymer solar cell of claim 1, wherein the second polymer surface is an incident surface of lights.
 13. The polymer solar cell of claim 1, wherein the second polymer surface is positioned to receive incident light beams, so that the incident light beams reach the photoactive layer from the second polymer surface. 